From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Temperature-related inaccuracies in A.T. speedometers and the recommendation to fit a modified version.
| Identifier | ExFiles\Box 50\4\ Scan127 | |
| Date | 13th July 1927 | |
| X4308 To BY. {R.W. Bailey - Chief Engineer} from Hs {Lord Ernest Hives - Chair} /Rm. {William Robotham - Chief Engineer} c. to Roy. {Mr H. Royce - Buyer} c. to Hm. {Capt. W. Hallam - Head Repairs} c. to Mx. {John H Maddocks - Chief Proving Officer} Hs {Lord Ernest Hives - Chair} /RmL/LG13.7.27. A.T. SPEEDOMETERS. We have been conducting tests on the A.T. speedometer as at present standardised and find that its reading varies considerably with its temperature. Actually, if the temperature of the instrument board rises 10°C, the speedometer will read some 5% slow. We have taken up the matter with the A.T.Co., and they have incorporated modifications in their instrument which have very largely overcome the trouble. We consider that it is imperative that these improvements should be incorporated on our present production speedometers as soon as possible. In the case of cars used in tropical climates where the atmospheric temperature rises to well over 30°C, the speedometers will read as much as 15% slow, in extreme cases. We therefore recommend that in the case of any complaint as to inadequate maximum speed, one of the new type speedometers should be fitted. Attached is an approximate curve which demonstrates the error in the present speedometers which we have been investigating. Hs {Lord Ernest Hives - Chair} /Rm. {William Robotham - Chief Engineer} | ||